So I have been battling a vibration ghost.

My wifes 2003 S60 with 130k started to vibrate when accelerating, usually in 5th gear (automagic), about 6wks ago. It started as something soft and occasional, so we did like all owners and ignored it. After a week or two it got real bad so I threw the car up and found a collapsed front mount. I replaced it and the vibrations did not go away, but reduced significantly. They started coming back this week so I checked the mount I had installed...collapsed (stupid internet mount). The upper mount was also toast. So 120$ later I have two locally sourced Hutchison mounts and I installed them yesterday. HUGE difference at idle and at low speeds, gone is any sign of vibration. Now there is a distinctive vibration (with a rubber dampened feel) when accelerating between 55 and 65-70 mph. the moment you let off the gas or decrease the rate of acceleration it goes away. I am good at accelerating and not getting it to happen, my wife is good at getting it to happen.

So WTF!!! The two new mounts and the torque limiting mount (center front of car between sub frame and engine) are all new. The fluid filled mount located behind the front grill looks good (not leaking) and I can't see the other mount, but there is no fluid stain on the sub frame below it.

I am at a loss. could the T-belt have skipped a tooth? Could the tranny be going? I know I need to replace the pass side tranny side drive shaft boot, which is torn, could that be it? Maybe something drivetrain and not motor mount?

Any thoughts, suggestions, or insight would rock.