I have some mics in aluminium tubes (10mm diameter inside - 12mm outside). Using some of then I have found strange lines in the spectrogram, not always, it took me some time to discover that it was because of the pressure I put on the mics, they are very sensitive.
If it is very tight it can cause strange lines, in case you find any, you know why it can be ;-)
All my future mics will be encapsulated with no pressure around it and with electrically non-conductive material. Silicone is one option, plastic tube is another one, and cable gland PG13.5 another