Mach 1 Funny Noise from the Mach ???

DOHC otto said:

My car is making a really weird noise after you start it and it is at high idle for about 20 seconds it makes a loud thump coming from the bottom of the car. Only does it once and only when the car hasn't ran in a few days. Temperature outside doesn't seem to effect it. It kind of sounds like someone hit the bottom of the car with a bat. Seems to be coming from the passenger side by the mid pipe. I got under the car and no scrapes or dents around any of the exhaust. If anybody has a clue what it could be please help me out .

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Mine makes a similar noise if the AC or Heater is on.

from: http://www.mach1registry.org/forums/showthread.php?t=59200
Yep. Welcome to the world of the infamous A/C thump. There is a TSB on it, and it is the hose shifting when the compressor engages. You can actually fix it yourself with some pipe insulation and zip ties. Look at the right side strut tower and the hose right next to it. When the A/C cycles the hose shifts and thumps againt the strut tower. By wrapping the hose in the pipe insulation it keeps it from shifting as much and muffles the noise. Hi-tech...eh?

* TSB #17531 -- THUMP NOISE WHEN A/C CLUTCH ENGAGES. *MJ (NHTSA ID #10008103, FEBRUARY 01 2004)
* TSB #17286 -- THUMP NOISE WHEN AIR CONDITIONING CLUTCH ENGAGES. *TT (NHTSA ID #10004930, OCTOBER 01 2003)
* TSB #02208 -- CLIMATE CONTROL A/C SERVICE TECH TIPS. *EH (NHTSA ID #10013060, OCTOBER 14 2002)

HTH

No Problem