When i accelerate after i stop sometimes my left wheel makes a knocking sound.

What is your question?

Its an '02 Buick Century Limited, 70,000 miles. It doesnt happen often except for when ive been driving my car all day. Im about to drive my car 1,200 miles. I just wanna know whats going on and if i need it to get fixed before i leave. Ive taken it to two different mechanics the first one said I have a lose motor mount and the other guy said nothing was wrong.

What makes this problem better or worse?

Acceleration

How long has your 2002 Buick Century had this problem?

Month or so