Hi!

It seems that all new dehumidifiers are junk. I don't know. I have two
vintage units--one a Ward's Signature brand and the other a Sears
Coldspot--that are going on 40 years old now and still work perfectly.
(The Signature lost its low fan speed about ten years ago, but who
cares? Who would blame it? The Sears unit has only needed a new fan
motor...while the overflow cutoff is bad, it empties into a drain and
I don't care about the long defunct neon "full" indicator.)

As to your problem...check the rubber mounts on which the compressor
lives. There should be four or so between each "foot" of the
compressor and the frame of the unit. If those seem to be OK (and the
fasteners are reasonably tight), check the fan motor and its blades.
The motor could be loose or the fan blades might be hitting something.

If you can, try to run the unit with the cover or grille(s) off to see
what is making the sound. Exercise caution before touching anything
inside to see if you can change or eliminate the rattle.

William