Noise when peddling hard uphill

I had a weird knocking on my bike that would only occur when I was out of the saddle and found that one of the bottle cage screws was loose on the downtube.

+1 on checking for dry joints on cranks / pedals, etc, and even just greasing them as a precaution.

i always hear really loud breathing whenever I go up hill.

My bike makes a sort of groaning, wheezing noise every time it goes uphill...no - my bad...that's just me...
Take it to a bike shop and get it a general service. Pretty sure it'll alleviate you of some money..but not necessarily rid you of the problem...friend of mine had the same problem with a brand new Canyon (Ultimate CF SLX9.0) with a campag gruppo....was that dreaded (Ultra-torque?) BB ...and no campag tools to use to inspect it...and mail order....but Canyon 'vouchered' him to have it looked at from a LBS....so it wasn't all bad...LBS said it was the threads creaking and a bit of copperslip/silicon grease sorted it out....so hopefully that's all you need...

Bit of a long shot this, but I once had some pretty weird noise that I couldn't diagnose for a while, which turned out to be a worn small chain-ring causing some unpleasant friction with the chain. This only happened when I stood.

One replacement chain-ring later and the noise had gone.

Of course you could argue I was clearly using the small ring too much to wear it to this state. Alas, you're probably right.

I seem to get a funny rasping sound when going uphill. It starts somewhere in my chest but seems to spread to my mouth.

On Tuesday I heard a strange creaking sound which I thought may be coming from the bottom bracket, but today I rode a different bike and heard the same noise.

When out of the saddle the noise stopped. On Tuesday I wore a new pair of shorts for the first time and I now realise the noise came from the pad.

So it was, in a way, the bottom bracket.

I had something similar with my BB, just screwed it off, degreased and cleaned everything then re-greased and was solved. There Was a surprising amount of gunk internally!

I had something similar with my BB, just screwed it off, degreased and cleaned everything then re-greased and was solved. There Was a surprising amount of gunk internally!

I agree with mike the bike.
A bang is sometimes a real problem

A further test is to hold the left and right pedal and try to wriggle them laterally. Not up and down in the pedalling plane but left to right. There should be no play (movement) at all. If there is any movement you need to take a look at the BB asap!

You don't say what type of bottom bracket you have

Recently I had a problem with a pronounced "click" under load with a square taper BB. I removed the BB and pedals, cleaned everything and used *lots* of grease to reassemble. It is nice and quiet now.

...or then again it may just be your knee joints!

I'd have said BB as well BUT I had the same last week and replaced the chain! So worth checking ti, its cheaper and easier to replace.

get the bb shell faced as well ...

A creak is usually a sign of dryness; pedal bearings, BB bearings, it could just be a dry joint where the crank arm sits on the spindle.
If it's a banging noise and you wince every time you hear it, it could be a bearing.
I'd start off by lubing everything up, a small amount of grease on pedal threads, crank spindle and crank bolts. Whilst you have the crank off give the bearings a turn with your fingers. Everything should feel smooth, with no signs of jamming or play. Once everything has been lubed and the noise still persists it's time to look at new bearings.

Vague noises are 'orrible to diagnose correctly but here are some ideas ....

Check tightness of pedals.

Temporarily swap pedals for another pair and see if noise goes away. If so you know what the problem is.

Check tightness of cranks and, if yours has the dreaded Shimano lock tab, make sure it's in position.

Check tightness of BB.

And finally, try another BB. A good Shimano replacement should cost only about £15.

Best of luck.