Alba Digital Micro system clicking loudly when playing cassette tapes

I have an Alba Digital Micro CD/radio/cassette player system, the model number I think is SYS1717CD. I hadn't played tapes on it for some time until now as it was packed away for several years. The radio and CD parts seem to work fine but when I play audio tapes there is a loud, fast clicking sound which persists the entire time it's in use. I've tried two tapes and have run one of those cleaning tapes through it (I was dubious as that itself was pretty old) and am at a loss as to the cause. I haven't yet tried taking it apart as I don't have the manual for it and don't want to lose any bits.