Four possible sources / problem areas of which I'm aware, listed in order of usual probability:

1. The belt tension pulley assembly.

2. The main drum bearing (on the right side).

3. The drum air duct bearing (on the left side).

4. The motor.

A potential clue to the source is whether the rhythm of the noise seems faster than the tumble speed (1 & 4), or about the same as the tumble speed (2 & 3).

This service manual is not an AeroSmart model. AeroSmart has a different control panel, but the mechanical design is the same. There should be a Tech Sheet in your control console outlining how to access Diagnostic Mode.
DEGX1 / DGGX1 Service Manual

HI--thanks for sending this info & for the manual.

My husband tried something on the right side. It made the sound not so loud, but still there. Since he is working about 60 hrs a week, he said go ahead & call a serviceman. He came & said he would have to order a $0 ball baring, but the dryer was OK to use. As soon as he left I did a load of wash. When I turned on the dryer, it immediately turned itself off & it says Fault Code 21. Call for service." I even had to roll the drum & hold that tab on the left to get the towels out. Do you know what Fault Code 21 means & is it caused by something he did?
Thanks.

I thought to check the manual you sent. It says: Door Actuator Required Excess Voltage. Could this be caused by him taking the dryer apart &putting it back together incorrectly, or is this another problem altogether?

Thanks again.

Something is putting a bind on the door grabber motors. Could be caused by misalignment during reassembly.