Noise from the back

[TaxMan]

I hear a weird noise (a high frequency noise - as if you struck a tuning-fork) comes from the back of my car at around 2500 RPM. I hear it only after a cold start and it disappears after driving for about 5 mins. Does anyone else have this problem?

[IIx 03 EP xII]

i have a similar noise... it sounds like a window being tapped with something like a fork... but it doesnt always go away... its there sometimes... and sometimes its not. my friend said its my muffler loose or something... so im gonna get it all checked when it goes in the shop for a few repairs from an engagement with a 65 mph landscape rake.