Unexpected noises, such as you describe, can sometimes be caused by the adhesive that holds the iPad's battery to the unibody chassis - or the adhesive that attaches the iPad screen. Noises from these sources cannot be assessed remotely - but can be identified by physical inspection.
Your iPad, purchased from an independent retailer, still has a warranty. You should, in the first instance, seek assistance from your retailer - who may replace the iPad.
Alternatively, you have benefit of Apple's limited one-year warranty that also covers manufacturing detects. To explore this avenue, you would be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to assess your iPad. If a defect is confirmed, you will be able to explore your available options for remedy.
Genius Bar Reservation and Apple Support Options - Apple