In the absence of recent penetrating trauma, at 8 months post-op this is NOT air inside your pocket--any air introduced during surgery was completely absorbed over 7 months ago!
Your implant sliding against adjacent moist tissues causes a friction rub (sound) that can be felt as well as occasionally heard. This is termed "bourdonnement" and was definitively described in the plastic surgery literature: "Bourdonnement and other benign temporary breast implant sounds", Annals of Plastic Surgery, Vol 43 p589, 1999. Typically this occurs in the immediate post-operative period and resolves without treatment in a few days to weeks.
When this occurs this long after surgery, the sound is not related to the incompletely-healed and still-inflamed tissues. It may well indicate some new source of inflammation, possibly related to a moderate trauma to the breast tissues, perhaps secondary to bacterial contamination such as from dental work (controversial, but still a real occurrence). The inflammation that causes this sound may also be related to a recent viral illness such as chest cold or influenza.
A friction rub heard on chest auscultation with a stethescope can be associated with a pulmonary embolus from DVT. Bourdonnement alone without any other symptoms (leg pain, swelling, shortness of breath) is NOT worrisome.
Ibuprofen or Celebrex (prescription) anti-inflammatory medications are a good starting point for treatment. If you begin to notice firmness or soreness in the "noisy" breast, this could be an early sign of capsular contracture. See your surgeon for evaluation and consideration of a course of Accolate or Singulair and Vitamin E. Best wishes! Dr. Tholen