We have an older Jet 37" single belt wide belt sander. In general it performs ok but it's far better than not having it.

Occasionally I get chatter marks when using it that show up as lines roughly an 1/8" wide about 1/8-1/4" apart running across the width of the material. It is worse with glue ups than with standard flat stock. It appears worse when I try to put more than one piece through at a time.

Today I was sanding 2 glued up boards of red oak about 6" wide made from 6 - 1" rips. Sending one board through at a time it worked fine, send two boards at the same time and I get chatter mark and a noise that sounds like chattering.

Any ideas on what might be causing this?