Whistling Sound From Engine

I drove my Speedy up to Vermont this past weekend, 4.5 hours each way and she ran great. Even managed to keep up with the traffic on the Thruway. While I was driving I heard a weird high-pitched whistling sound coming from the rear of the car. Couldn't pinpoint the source exactly but I'm guessing it was from the engine bay. It sounded like a tea kettle coming up to a boil and started exactly at 3500 rpms right up to 4000 rpms, which is the highest speed I ran the engine at. When I let off the gas and the rpms fell below 3500 the sound stopped.

Any ideas as to what this is?
I had the car tuned up the weekend before and the mechanic gave her a clean bill of health.

Fred,
...probably the carbs sucking a large amount of air at hwy speeds, some carbs ( Delorto and ?) have a replacement base gaskets to eliminate the whistle....."just go faster and see if it goes away :)

I'v heard noises like that before and it can be a whole list of things to include a piece of paper stuck in the fan, fan belt too tight, an intake leak that only shows up at high RPM's, a bad bearing or bushin in the alternator, cam gears (do you have straight cut gears) a bad rod or main bearing that only makes noise at 3,500 RPM's, a breather hose that's crudded up and under pressure it sounds like a whistle. Carb's that only make noise at that RPM
Something stuck in the exhaust system that vibrates or makes noise only at 3,500 RPM's. A fan that's hitting the shroud and making a noise?? As you can see, the list is long.

I have Del carbs and they whistle dixie at high speeds

Wow Larry - That's one hell of a list!
Maybe it's just the sound of happy Kadrons urging me to go faster :)
I'll have a look first at the obvious things on Larry's list.
Thanks Guys!

Fred - post a pic of your engine set-up! It might help with trouble-shooting (maybe restrictive air filters?)

Here is a shot of my engine - I don't think the filters are restrictive.

Fred,
What I like about your car is the simplicity of a stock 1600 engine... totally reliable motor and a care free driver, just hop in and go.

Alan,
I agree; the beauty of the car is matched by the simplicity of its engine. And the best part is my engine whistles while it goes!

Could it be that what you're hearing is the normal whistling of the VW fan but more of it and sooner in the rpm range because you have a smaller diameter 356 pulley on the alternator?

Fred:

Larry's list is pretty complete, and I won't be adding to it, but try this first before you tear into the others:

I suspect a leaking intake manifold gasket. They are notorious for leaking on these cars, because there is a long torque arm made up of the intake manifold and carburetor on top, it vibrates a little because of the length of that structure causing subsequent pounding of the lower gasket and premature failure.

Get a can of carburetor cleaner and, with the engine idling, spray it liberally around the manifold base gaskets where it bolts to the head. Do this on both sides and see if the engine idle speed changes during the spraying process. If it does change, then you've got a bad gasket where you were spraying and will have to change it.

If it doesn't do anything on the lower gaskets, try the same process on the manifold-to-carburetor gaskets.

If nothing happens to the idle there, then move on to the next stuff on Larry's list.

gn

Thanks Gordon, I'll start there. What did you think of the Stratton show? Sorry I didn't give you a buzz, I left your # on my office computer.

Fred, the last time this question was posted a person found an extra washer had been left on the head preventing the manifold from sealing. I personally don't think this is it as "usually"
(I said "usually") your engine would hunt at idle(varies up and down). But the starter fluid spray will let yuo know for sure. Also at idle your have a higher vacuum on that gasket area, when you open the throttle you have less vacuum on that area. ----good luck!

That's why I thought it it isn't an intake leak; if the engine's operation isn't compromised in any way it's more probable that the problem is elsewhere.

Maybe the car is happy and just whistling a tune. Could you make it out?

A while back my car started making sounds like a loose fan belt....chirp chirp chirp chirp.....fan belt was not loose. Drove it for a few miles and tightened the fan belt even though it passed the 1/2" deflection test.....chirp chirp chirp.....drove a few more miles and it then started chirping worse then backfiring when ever the throttle was not depressed..... that is 99% of the time an intake leak, and yes, that is what it was this time too. Tightened up the bolts on the intake at the head, presto, no more chirp and no more backfire.....until it started the backfire I would have sworn it was a fan belt problem, had checked alignment, tension, pulley running flat and concentric, and had started considering replacing the fan belt....

Oh by the way, the standard VW intake gasket (metal with a seam that compresses) may be fine for a stock VW engine, but a good aftermarket gasket by one of the major vendors is much better for avoiding leaks in the first place, or better yet use a thin bead of hi temp (copper) silicon gasket and be done with it. One thing to avoid is leaving the hexbar linkage on the carb while you torque down the intake manifold. Fairly frequently the linkage will keep the manifold from seating properly....if it is too long it is almost guarenteed to cause a problem.....

Fred, some time ago I had my fan explode, before this happened there was a high whisling sound coming from the engine. Replaced the fan,shroud, altenator stand also added a altenator pully w/ fins put it together and I still had a noise, more suttle thought it was the fins? wrong Larry figured it to be the altenator bearings had them replaced(confirm groove wear)installed balance race fan and everything feels as should. Cabanaboy ~ hope this helps