Horrible noise (when standing)

Check your chain for any cracks int he side plates. I have had two KMC ten speed chains go and the symptoms were very slightly dodgy shifting and occasional cracking noises when standing (i.e. putting alot of power through the transmission)

grit in the bb area, take it out put plenty of good crease in it and that will sort your problem.

Creaking and cracking will be the bottom bracket area normally neglected by manufacturers with fitting cheap sealed units (out of sight out of mind). Remove the chain off the chainset (onto the frame) does this still spin nice and smooth/silently? Maybe worth stripping this out of the frame and re-grease both frame and BB threads. Also worth applying a little grease to both pedal threads before fitting back into each crank arm.

could be a loose spoke too

I had a similar experience recently, checked all sorts of things including the things that Trikeman suggested. I ended up taking it to lbs and they checked the bb, but it was the chainring bolts in my case. Also worth checking the seat post and saddle clamp, even if it doesn't occur when standing. A blob of grease doesn't hurt
Lastly this is pretty helpful - http://www.jimlangley.net/wrench/keepitquiet.html

Hi,
Just a few quick checks.
a. Check pedals are tight to the crank arms.
b. Check chainring bolts to the cranks tight (the ones that go through the cranks/chainring front gears.
c. Check crank arm(s) to axle are tight.
Let us know if all these are tight/secure first off.

Regards and hope this helps.

Trikeman.