Is this normal? This only seems to have been occuring since I had my last service.

2003 Nissan Skyline RHD 350GT Coupe - NISMO exhaust | K&N + Custom pipe | 19" rims | Nissan HID fog light kit | folding mirror kit | reverse cam kit | 35% black tint

Just an oil change and minor service. I also had the AC belt and bearing changed as it was wearing, but a part from that, nothing unusual.

The car has also taken on a deeper growl from both the engine and exhaust. Doesn't sound bad, actually quite the opposite, but this was related back to the belt change as before I had a very noisy belt.

Good news is that if it was a major problem, you'd probably have some indicator lights.

Check around for vacuum leaks from the AC belt change (they may have disconnect items to get to it).

+1 This is probably the issue. I've also seen dirty Throttle bodies do this.

Let the car idle and listen for and air leak sounds.