Tranny Cover vibrations

So is it crappy repro transmission covers ( 727 small block 71) that are causing the insane vibrations as I drive or is something else the culprit?

I replaced the missing cover , tightened everything down, no missing bolts an drove the car , it was fine.
Getting off the parkway and merging into traffic on road, I start hearing insane vibrations, so bad I think the transmission is about to blow. I gingerly drove it to my mechanic down the road (was going for an inspection).
He put it on lift and started car, and it was definitely the cover making the god awful noise. All bolts were secure.
Is the metal on the new covers just cheap and thin?
My other 71 with same cover doesn't vibrate at all. Not sure if it is a repro or not.

Are the convertor bolts hitting the cover?

Yes, I seem to remember some little fingers on the cutout by the crank hitting if they don't seat right.

You mean the 2 small bolts at the bottom that act as a cover for the smaller inspection plate?
Was thinking about them as well. I was going to try and take them off first to see if that made a difference.

This.

Incorrect, bent or warped cover, cheap plastic cover, loose converter bolt, incorrect converter bolt. Correct converter bolts have thin heads and DO NOT use washers of any kind.
Cracked or bent flex plate.

Myself, i usually run without them. If you find one that doesn't make noise, you should go to church on Sunday
Do be aware that there are two different covers depending on the flexplate to converter bolt circle.

Its easy to tell if its the cover, remove it and check for wear...but then again it would of hit and make noise on 1st start up..its not like it bends later

Exactly, not sure why it was fine for half the trip and then suddenly start vibrating. It didn't look cracked or anything when we inspected it on the lift.
I'll get under there today and check it out, thanks.

Or the crank thrust bearing is severely worn.

I would remove the cover and look for a loose or missing converter bolt

I removed the cover, didn't see any noticeable wear, and it wasn't cracked or anything.
I will check the converter bolts, good idea .

Everything was tight and no sign of wear.
Just going to leave the cover off.

My cover would make noise until I shimmed the two lower bolts with some thin washers. I had no noise after that. I assume the cover must have been tweaked a little.

Didn't make sense for me to shim the lower bolts, especially on a brand new cover, but glad it helped.
If I put it back on, I'll see if that makes a difference