As far as redeeming your copy of Beat Saber goes, it should actually be pretty simple! Once you activate your new Quest 2 on your account, you should get an email that has a link to follow to redeem your copy of Beat Saber to your account. (If you don't see it in your inbox, make sure you check your junk/spam folders too.) Once you do that, you should be able to install it on your headset!
And as for hearing crackling from your speakers... That definitely sounds like something you should submit a support ticket for.
Let me know if you have any questions or anything. Happy to help! 😁