Lukewarm water in Kitchen Sink and Noisy pipe

RaulDublin

I have a question for some plumbing gurus if they can help me figure out the nature of the 2 problem .

The hot water on our kitchen sink tap is lukewarm and I realize that it has never been as hot as the other taps upstairs . I say never since we've bought this house 2 years back so dont know what was the case before .
Water on the taps upstairs and the shower is quite hot when we have the hot water running for an hour .

Also of late I notice a squeaking/rattling noise coming from the pipes going into the attic or in some of the pipes in the attic when the toilet is flushed . This was not the case when we moved in .

Radiators are working fine and I can read between 70-80 deg on all the rad panels when the heating is turned on upstairs and downstairs.

We have an OFCH with a firebird enviromax boiler which is 3 years old . Had got the old GB pipes removed and all the heating system re-plumbed with new radiators and new hot water cylinder before we moved in late 2017..

The plumber who did the job has moved elsewhere since and i cant reach him ..so any tips would be very helpful before I scout for some local help