Hoover TC-650 tumble dryer is hard to get going?

When I press the 'On' button the machine will just start up but if I just press it and let go it will stop right away. I need to hold the button in for a variable amount of time before it will go properly.

While the button is held in there's a noise that comes from behind the panel and only when that noise goes off does the machine not need the button held in. I don't know if it's a chattering relay, arcing or whatever but I can hear it over the rumbling of the drum moving and it's a higher pitch noise than that.

Once it's started it seems to do the job ok. It makes no difference if the machine has been off all day or on all day. After it's finished a cycle I'm back at the start with struggling to get it to start again.

Any ideas please ?

Thanks