IIRC, it's fairly common on many of the IRS Cobras. Mine makes a "thud" sound if I am at rest in neutral and put it into gear (most noticable from 1st into 2nd).
You may also experience the "clunk," where you are cruising along, lift off the accelerator, and then step back on it - you will feel a "clunk." I *think* that issue was due to driveline slop...
It's been awhile since I remember these questions being asked on the message boards by 99/01 owners who just purchased their cars at the dealer...wish I could help more.
I appreciate the response. At least I now know that it is a common issue. I would like to ask you some more questions if possible? What was the problem with the 99 cobra HP wise and what did SVT do to fix it in 01? Also what are some of the problems in the 01, what can I do to fix them?
For the 99 horspower "fix" info, check out TXsnakecharmer's webpage - it is one of the most comprehensive
99/01-specific webpages out there on the 'net.
The '01s did not experience any widespread problems like the '99s did. However, a handful of '01 owners have experienced pinging/detonation in their engines while under load. Some folks tried switching to one heat range colder sparkplug and letting Ford do a factory
re-flash of the computer/PCM. Ultimately, there never really was a *magic* cure for the "ping."
TR-3650 transmission has been "hit or miss" (but this issue extends to all other Mustang models which were equipped with the TR-3650 trans - newer GTs, et al). Visit the "sticky" thread in the 4.6Tech section to read all about the TR-3650 problems...
Other than the small numbers of "pingers," the 01s were a good build year for Cobra production IMHO.