Guitar amplifier. When I turn on my marshall amp it makes a strange sound which resembles a small

Question

When I turn on my marshall amp it makes a strange sound which resembles a small motor. it has only started making this sound recently, before now the amp was silent. the sound on the amp is good but it just makes this weird noise. can you help me?

The amp is a marshall and the model is : Valve State 2000 AVT. It is a 50 watt amp.

Please help me if you can.
Thank you.