Subwoofer not working after HDD have been replaced with SDD

Greetings,

Today I was helping a friend to replace his HDD with the new SDD he bought for his mid 2012 Macbook pro 15. We also got a caddy to replace DVD with old HDD, thus leaving him with two discs (I have already done this couple of times on different macs). After we finished, everything was working fine, both discs running smooth etc. However, after playing a song from iTunes, we noticed that there is no bass whatsoever in the playback. We both are audio engineers and know frequencies pretty good, so everything below 200 Khz cannot be heard. We tested the built-in output with the headphones we are familiar with, and it is working normally. Then we made A/B test with Macbook pro 13 and this particular 15 I am talking about - low freq. are apparently way more transparent comparing to 15, which is insane. So, we checked the positioning of the speakers on the board and figured out that there is a woofer just next to the HDD slot. However, we were careful and did not pull anything or made any physical impact that would kill the woofer.... any ideas or similar experiences? Thank you in advance, he needs his mac ASAP, it is our bread and butter 😉