Which boiler model do you have?
To replace a heat exchanger could be a costly venture
Options (cheapset first) To add a noise silencer like a Fernox F2 to reduce noise.
Another option would be a powerflush of the central heating system, using a powerflush unit and chemicals like Fernox DS-40 and system neutraliser.... then fit a magnaclean filter (Professional or TwinTEch) 😉