Squeal from front-end after long drive?

[dammad]

I just drove from the Bay Area to Lake Tahoe in my 99 996 convertible. After the drive, I stopped and heard a loud continuous squeal from the front-end of the car while the engine was running. I turned off the AC and the squeal remained, but stopped when I turned the engine off.

There's not much at the front of the car to make such a noise especially when the fans are off (AC off, coolant temp between the 8 and 0 on the temp gauge).

I videoed the front of the car to let you hear the squeal. It seems louder behind the wheels and perhaps on the passenger side.

I had this once before after a drive to Yosemite but was unable to track it down.

Sounds like a pressure relief valve or leak??? Could it be the increase in altitude? 1000ft --> 5000ft

Any ideas?

Edited January 5, 2012 by dammad

[Loren]

Sounds like something is hitting the fan on that side.

If it were more centrally located I would suspect the fuel pump.

[logray]

+1 to the above.

To diagnose further I would remove the wheel well liners.

Also lift the hood and remove the cowling near the windshield.

Between those simple steps it should be easier to isolate where the noise is originating from.

[dammad]

Thanks for the pointers. You guys are the best!

The fans weren't going, so I'm assuming its the fuel system. I'll take it on a long run to try to replicate and isolate the source.

[fpb111]

Did you open the fuel cap while it was making the noise? To rule out the evap system.

[dammad]

Alas I didn't think of it. I tried to reproduce (long fast run down from Tahoe to Bay Area) and was unable to replicate. Perhaps it was a change in altitude thing?

[Orient Express]

Fuel system pressure equalization valve. If you had opened the gas cap, it would have gone away immediately. Normal.

[dammad]

Great good to know. Just to double check: Would the pressure equalization valve stop squealing when the end is turned off? I assume the pressure in the tank changes at that point.