Toilet/waterflow problems.

Hi. Was wondering if someone can help me with a loo problem.
When we flush our downstairs loo it makes a noise like a boat going out to sea and it's actually quite loud. However, we have discovered that if we turn on the tap in the sink in the same bathroom when we flush the loo, that the noise stops! Our electric shower has also almost given up the ghost. Before it was hot on the 1st setting, now we have to whack it up to to the 2nd setting on high and it may or may not be okay. I have started using a hose on the taps in the upstairs bathroom because at least I can control the temperature there. Is it just coincidence re the shower or is the loo problem connected to the shower.
There is no shower in the upstairs bathroom and everything works fine up there.

Usually we replace the w/c cistern ball valve washer to solve cistern filling noise problem

Thanks for the reply but is that all it will take to stop the noise? How is the water flow in the sink connected to reducing the noise and does it have anything to do with the shower problems? Thanks again.