Clicking sound on each rotation of the pedals only when riding Let me prefix this by saying that I don't know much about bikes. Especially from the terminology perspective.

When riding, I can hear a relatively quiet click when I push down on the pedals. It happens when either of the pedals are in the upwards position, even when I try to put on continuous pressure during the whole rotation. I also feel a slight vibration when it clicks.

It seems to me that the sound is coming either from the pedals or from the part where they're attached but since I can't reproduce the issue when I turn the bike upside down, I can't pinpoint the source.

This started happening a couple of weeks ago. In the mean time I took the bike in for regular maintenance and it seemed to fix the issue but it came back the next day, or the day after.

What can I do to diagnose this issue? Should I just take it back to the repair shop, or is this something I can fix myself?

The bike is Ghost Kato 2.9 if that matters.
While everyone here suggesting the bottom bracket is the likely culprit (and they're probably right), I wanted to comment nonetheless and point out that this could easily be the less common issue of worn bearings in one of the pedals.

Try rotating the pedals with your hand. If they don't spin smoothly, that's a good indication that you've got a bad bearing. You can try taking the pedal apart and repacking the bearings/grease, but odds are the track is pitted. The pedal will continue to fail. Unless it's a clipless or expensive pedal, just buy another pair. They're cheap.