"clunk" noise upon pressing or releasing gas pedal

[bigcars]

Hello. I just picked up a 2005 Crown Vic LX Sport with about 36K miles a few weeks ago. When coasting along at 30 to 40 MPH, and the gas is pressed to accelerate, there is a distinct “clunk” noise that originates from under the car. The noise happens when initially pressing the gas pedal and then again when the pedal is released. Anybody experience or hear of anything similar? What would you be looking at first?

[timmn1]

The first thing I'd look at are the engine and transmission mounts.

[bigcars]

Thank you for your recommendation. Here’s what my local ford garage has come up with so far. Long story short, they identified a noise during their road test of the car, but it apparently wasn’t the same noise I was hearing. Their diagnosis was that the backlash was excessive (measurement of 0.018). They pretty much rebuilt the rear end of the car, but that didn’t fix the original concern that I described. Fortunately, the car came with a warranty, but I’m concerned where things are headed as they’ve already sunk a good bit of money into it.

[jad0110]

Is it coming from the rear axle? I had a '95 Chevy C1500 that would do the same thing. Whenever it started clunking, I'd have the U-Joints lubed and it would cure the problem, usually about every 10-15k.

[bigcars]

I can’t tell exactly where it’s coming from. The dealer put chassis ears on it and concluded the sound was coming from transmission. They tore it down and replaced the direct clutch. That didn’t eliminate the noise. Their conclusion is this: We checked the entire drivetrain and replaced everything that was out of spec. They believe noise “to be nature of the vehicle”. They have openly stated that they still believe it is a drivetrain noise, but they’re now insisting that they need to compare a vehicle with the exact same transmission and rear end. Issue #1: It’s going to be tough to find another 2005 Crown Vic LX Sport (or a 2005 Crown Vic LX with the Handling and Performance Package) around my area. Issue #2: If we find a comparable vehicle and it exhibits the same noise, that doesn’t make the noise “common” to that vehicle. (i.e. Two vehicles exhibiting the same characteristics out of hundreds doesn’t statistically make it common to those vehicles). Issue #3: If we were to clearly establish that the noise was common to most or all of these vehicles that doesn’t automatically mean that the noise doesn’t warrant some current correction or won’t warrant some future correction. Issue #4: If the comparable vehicle doesn’t exhibit the same noise, they weren’t able to say what course of action they would take. So now I’m looking at working my way up the ladder at the dealer and with Ford Motor Company.

[drwyczalek]

Try checking universal joints on driveshat probably got a bad one if it gets real bad it will also cause a vibration inside car driving down road