A leak or pipe noise?

[pineapple]

After running the 1st floor bathroom washbasin tap for upwards of 6/7 seconds (hot or cold) down an unplugged sink there is a drip noise from underneath the floorboards. I say 'drip' but it is also similar to the 'creak/tick' noise that pipes can make. It also happens to a lesser extent when emptying the (very small) basin.
It's generally faster at the start then gets slower - till it peters out after a few seconds.
There is no noise after running the bath.
This could have been happening forever or just recently - but I only just noticed it.
There is no sign of any leak downstairs though since noticing I don't use it very often - I'm too afraid to!
Before I get in a plumber to rip apart my bathroom are there any checks I can make?

 

[Blagard]

If the noise peters out while you continue to run the water then I would suggest it is simply pipe noise of a pipe rubbing as it expands and contracts.

As there are no signs of a leak I would probably do the opposite to you and flush loads of water through (you might call that a soak test!) and if still no sign of damp anywhere simply accept it is some pipe noise. One thing is pretty certain, it is not a leak on the hot or cold as this would be going on all the time maybe worse when water is off at the taps with full pressure in the pipes.