My lady's truck, an 04 GMC K1500, 5.3, 4L60E has begun making what sounds like chain slap in the transfer case. Shes got 291,000 kms on her, quite frankly I'm surprised the trans and T-case have lasted this long. The sound is 100% coming from the T-case. Same sound in 2wd, 4hi and 4lo. Possible...