noise and shudder

my Buick seems in good running order but occasionaly it decides to start a small shake or shudder with a very low end growl (also very quiet) between 45 and 55 mile per hour ive tried tranny flush oil change checked engine mounts( dont know why but thought it could have been that) unfortunatly the problem still exists. any ideas out there?

sounds like a torque converter lock solenoid is ssticking. Trans flushes and additives do little to free them up. Once they start to act up, they will just get worse. 45-55 mph is the approximate lock-up speed for the torque converter, and will cause a shudder when trying to accelerate from that speed if it doesn't un-lock quickly enough.

I just bought a 1995 LeSabre and it seems to be doing the same thing. The sound is coming from the front drivers side. To explain a little more detail...

From 20-25 I get a mild shake that I can feel in the steering wheel

From 55-60 I get a noise that sounds like a vibration when I'm lightly on the gas... if I take my foot off the sound disappears... if I push hard the sound disappears. The same sound will happen at 45-55 if I'm going up a hill.

Also on a side note the car tends to pull left and right while accellerating hard from 20-25.

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I've seen it suggested that this problem is....
lock solenoid
bad torque converter all together
CV joint (checked and no)
transmission shifting software
line pressure boost (fixed with pressure control solenoid)
some kind of build up in the torque converter causing to come out of balance