Gene, at the risk of not knowing which HWH system you have on your coach (mine is 610), the "clunk" sounds like one of the HWH relays is operating with the temporary shorting lead that is otherwise not operating. The 610 system should have a Master relay & a Pump Relay strapped to the pump motor. They operate in series meaning the Master relay must operate to pass power to the Pump relay which energizes the pump motor.
I use a voltmeter with 12' long clip leads (cheap & easy to find) to test the relays while trying to operate the jacks or room slide (or any slide). I prop the voltmeter up in the stairwell to watch while operating the HWH panel.
I start at the pump motor to determine if it's getting power but not operating. If it is getting power, and the voltage level is adequate, then the pump motor may be bad. Sometimes rapping the motor with a hammer will temporarily start it. You can use the generator or plug-in shore power and try your HWH system when the Inverter/Charge is in "Bulk" charge mode (14.5V or so).
If it's not getting power then follow the large red cable to the Pump relay. If the other large red cable on the Pump relay is not getting power then follow it to the Master relay. If the other large red cable on the Master relay is not getting power then check your front shut-off switch and batteries. NOTE: Low house battery voltage can also cause problems.
If you're getting power on one of the large red cables of either the Pump relay or the Master relay then that relay is probably not operating. The relay may be bad, or the control leads may not be working, or the voltage is too low.
If you find that the control leads on either relay are not working, then it's time to check the HWH control box. Of course, all of this assumes that the park brake is ON, the key is in the Accessory position, the chassis & house shut-off switches are ON, and the battery voltages are adequate.
Bob Bowers (Surprise, AZ)
2003 Alpine Coach 40' FDTS
2014 Jeep Cherokee Lattitude