Whistle when idle and changes when brakes applied.

[zrxinch]

Yes did search...
2001 ls8
started last week and is getting worse as the days go by.
getting a very high pitched whistle/whine at idle only when the engine is up to full temp, usually only after a ride on the highway. The sound changes and goes away when I press the brakes but even when holding the brakes comes back after a few seconds. Sometimes when tapping the brakes it goes away altogether. Pretty sure its a vacuum leak but I am not getting any idle or driving symptoms except maybe worse gas mileage. Checked all the hoses that are easy to reach, still have to dig and try spraying engine cleaner or starter fluid.
Areas I am considering from searching are...
intake leak (manifold) worse case....
Brake booster / egr splitter
any random hose or connection (haven't found any bad yet)

Any suggestions gladly welcome, I will most definitely post results when I figure it out, there are enough dead threads on this forum to fill a military grave yard and I don't plan on adding to that.
thanks in advance for any ideas.

 

[toby1234]

Like you said, most likely a vacuum leak. Anytime there is a problem that changes when you step on the brake pedal, it is most likely the vacuum hose to the booster. Could also be the check valve at the booster. Id spray some starter fluid like you said. Does the pedal feel more firm than usual?

 

[zrxinch]

Update... checked the tightness and "wiggled" the brake booster check valve.... noise hasn't come back since.. prob going to replace the check valve.

 

[toby1234]

Nice. Should be an easy and cheap fix.

 

[Blueberryyum02]

Also check the hose that comes from the brake booster I noticed that mines had a coupling in it that had a factory clamp on it I to took the factory clamp off put some worm clamps on it to get a better fit. Was thinking just do away with the split and run a straight hose.