I have have just acquired a Denon DRM-400 which produces a very loud clicking noise from one channel instead of picking up the signal from the cassette tape. I have tried several different cassettes with the same result.
The level meter on the deck shows a very high level on the faulty channel. The other channel is fine.
I am guessing it's a problem with the playback head.
First thing to try is to clean the pb head. A Q-tip and isopropyl alcohol will be fine.
Could be in the play electionic or head bias circuitry too. Not a DIY repair.
If you can't resolve this problem easily return the deck and get your money back. Cost of repair might be a lot more than you paid.