I moved into a new house almost a year ago. From the first day that I
moved in, the Hot water tank would rumble. It's certainly an older
(gas) unit and will need replacement in the near future, but I'd still
like to try to figure out variouis reasons that it might be rumbling.

I had first assumed that it could be sediment in the tank, so I drained
it, but didn't really get anything coming out during the drain.

The drain may have helped some, but it's tough to call. Since the
drain, over time, it has lessened. It used to rumble when you'd open a
tap or fill a bath, but it seems not to do it at those times so much
now. I just heard it rumble when the dishwasher was running.

Any ideas on the various causes that could be at work, causing the
rumbling?

I think I may plan to go to a tankless (gas) Hot Water Heater when this
dies, but I'd still like to try to figure out what's going on to cause
the rumbling in the mean time.

Thanks,

Danny