On this page (chosen as a random example of a picture, I have never used them): Hearing Aid Spares Pricelist - Domes
The top picture is of a “true” open fit dome, the one labelled “Phonak/Unitron power dome. Gridded” is a double occluded dome. In fact, “Siemens double dome for Life Models” is the exact one that fits the Reflex aids, it’s the one I have.
Regards the noise, maybe the noise is coming from the hearing aid moving around, try holding the aid still against your head when you chew or walk and see if it stops. If the aid has too much freedom to move around it will rub on your hair and head and make a noise, so you might need a shorter length of tubing on it or to experiment with where it sits on your ear, particularly if you also wear glasses, you need to figure out where everything is going to go. It may have nothing at all to do with the problem with the mould, it’s a bit of trial and error to work out where each problem comes from.
Find out what programs you have on your aid when you see audiology again, background noise is always difficult but there are programming options that make it easier to cope with. They tend to put on the minimum of stuff for a new hearing aid user as they reckon you have enough on your plate, and perhaps are not experienced enough to comment on what you want. It is a high cause of hearing aid rejection, however, so keep at it.
You will probably find you actually hear less well in your peripheral hearing, as digital aids are usually set to focus on what is in front of you, so if there is a washing machine, car indicator clicker, TV, train, whatever to your direct front and someone is talking to your side then it doesn’t work well for that situation. They should set the hearing aid at a lower volume on a first fit so it doesn’t overwhelm you, but NHS cost-cutting means they usually go for the full whack on day 1, which makes adjustment very hard. If you have a volume control (suspect the Spirit Zest doesn’t) then keep it down low for a few days, even if you think you cannot hear anything at all, it doens’t pay to rush into this process.