If you've had the work done then I'd take it back to the garage that did the work. If you bought it like this then I'd definitely be getting the timing checked properly before considering sensors etc.
I'd definitely recommend using your consumer rights. A whine which could be a gearbox, turbo etc is a major concern/issue. You could always get a second opinion regarding it's mechanical condition.
Or contact the motoring ombudsman
If bought in the last 30 days then I'd recommend getting it back to the garage asap for them to diagnose and repair which will be foc. You also have the right to reject the vehicle for a full refund in the first 30 days.
Welcome to the forum you'll find the members on here are a friendly and helpful bunch 🙂 as long as the gearbox has been well serviced then it should be fine.