I recently purchased this 78' z and was aware of the thumping at the rear end when I purchased it.  I replaced the rear struts, which were leaking.  I also replaced the strut mounts.  I have 16" tires all around.  The Nissan dealer says it's because of the over sized tires.  Is this true or do I have another problem?  I probably should explain further.  The thumping noise occurs on both sides when I hit bumps.  I thought it was because of bad struts.  When I replaced the struts the problem did not go away......  Thanks!

Edited December 31, 201510 yr by ynot1

Yes. The tire is oversized on only one side of the tire though%-0

Rotate tires around until you determine which tire is bad. Size should have nothing to do with this unless the tires are hitting the fenders.