TAW1957

My 93 has a slight whistling or hissing noise after warming up. I can modulate the noise with the gas pedal.

I checked the vacuum hoses that I could get to and replaced brittle or spongy lines.

I also have a new EGR valve installed, the noise almost sounds like it is coming from the trans.

Any thoughts as to what is causing this would be appreciated.

mnypitVette

might be your brake booster

Muffin

My first guess also. Second guess would be a bad hose in the HVAC system.

mnypitVette

One way to test the booster is to block off that hose and start it, go through the paces when you normally hear it. If you hear it, then its not the booster, if you dont then it is.

engle1147

A small hole (pin hole) in the exaust can cause a whistle as well.

TAW1957

Thanks to all for the suggestions. I'll try the brake booster test and go from there. I had the cats and 02 sensors replaced a couple of weeks ago, but the noise was there before and after replacement but I've never really inspected the exhaust beyond the cats, I only replaced both cats because one was OEM and breaking up inside and he other was a weld in generic. I replaced both with hiflow direct fits and new 02 sensors. I'll post what I find out tomorrow I appreciate the help.

huddo330

I had a whistling type of sound that I thought was vacuum related.
Turned out to be the rear alternator bearing on its way out. Might be worth a look !
Cheers

TAW1957

Ok, warmed the engine up, drove until I heard the whistle, stopped to plug the brake booster vac line, as soon as I pulled it the idle increased and the whistle came back, coming from the front of the engine around the pulleys and close to the alternator. Once the engine went beyond 200 degrees the whistle went completely away regardless of the rpm. I'll get some belt dressing tomorrow and see if that cures the noise or if it's the alt bearing. Thanks, looks like you guys nailed it.