My 05 Element has a knocking noise in the rear end. Could it be the struts, no oil is visible

Welcome, Kev05element.

Not much info to go on. The most common wear items in the rear are the stabilizer bushings, easy to check and fix. It could be the shock's lower mount bushing (p/n 52622-SCV-A01), one of the two rubber pucks (p/n 52725-S5D-A04), or the bump stop (52722-SCV-A02). Someone will have to take a good look under there to be sure.

Ive got alot of clunking too when I go over small bumps. I have been meaning to get it checked out, when I go to the dealer in 1000 miles.. I need to get them replaced soon because my warranty will expire in 13,00 miles.

Picked up a "dong" kind of knock last week that is now subsiding (think of a large rock thrown into the rear wheel well kinda of sound). Only did so on >50% of suspension travel on right rear after going down a very loose and wet gravel road. Sounded a lot like the strut was seizing a bit...I was hoping it was just some mud caked on from the muddy travel...but probably not.

Haven't heard it at all the last 100 miles though...kinda weird...gotta get under there to see what's up...driving dynamics remain the same but at just under 80k miles now, figure the suspension's weaknesses may come to visit any time.

it's the muffler knocking against the heat shield when going over speed bumps at an angle. i had my E in the shop for basic maint one time and told the mech about it. he looked and looked and figured that's what it was. we pushed against the heat shield to bend it outward just a bit and i haven't heard that knock since. try it.