| Knocking while accelerating
I have a 1990 525i. I have a problem that just appeared one day and I have just been dealing with it ever since. While accelerating under 20 mph, the car knocks fairly violently. It seems that it is coming from the center of the car and not from under the hood and I dont think from the transmission. The more gradual the acceleration, the less violent the knock. It seems to only happen under 20mph regardless of what gear it is in. After 20mph, you can accelerate as quickly as you like and it is as smooth as it could be. There has been a rare instance that the car drove fine one morning when the car was cold. That only happened once or twice and never since. I didnt know if that would give any indication to anyone on what the problem could be. I would appreciate any suggestions and thank you in advance to anyone who can help. | 
