Yes, FUD is the loudest noise
I had an ASHP installed earlier this year. I did all the pre-installation work (rads, plumbing, loft insulation, outside unit hardstanding) myself. There was a bit of Excel for rad sizing and just basic DIY*. If I had known then what I know now, I would have done much more of the installation myself.
The system just works - let the software do its stuff and forget about it. The only noise you hear inside the house is flow noise from the radiator circulation pump, which is programmed a bit OTT. I've seen the matrix frosted up in cold misty weather, but it clears itself and carries on.
If you expect it to do exactly the same thing, exactly the same way as a gas combi, you'll not like it. If you just want to be warm, with ample hot water, it's great. Same end, different means. I'm running on a 100% renewables tariff, so the real bottom line, carbon footprint, is infinitely improved.
*1960s cavity insulated house. It could be a bugger in a Victorian or older property.