Sears gas dryer model 417.93052300 super loud when heating.

Sears gas dryer model 417.93052300 super loud when heating. Replaced bearing assy with OEM parts, thinking that was the source of noise. Did not address the problem but now have new bearing! Further troubleshooting completed: When run with gas supply shut off, dryer is quiet. When gas supply on and dryer is heating, dryer is loud like sawmill - "wah, wah, wah, wah...." What do you advise?