Sounds like a spun rod bearing to me. Can't tell for sure without hearing it but from how you describe the noise it's a very good possibility. I spun a bearing about a year ago. It started out sounding like a chirp then turned into a knock. I was fortunate enough to find a stock crank on eBay for $60 + shipping that came out of a 6.0 Tahoe. I was able to do the crank swap without pulling the engine too. I was able to get the car back on the road for about $300. I chalked up the bearing failure to low oil pressure so when I did the swap I also put in a Melling high flow/high pressure pump. I wish I had taken pictures when I swapped the crank and did a write up. It was surprisingly easy doing the swap with the engine still in the car.
2009.5 Liquid Red - Premium - Red/Black interior
TVS firstname.lastname@example.org psi , ID850's, ZL1 Pump, Rotofab CAI, Kooks 1 7/8" Mids w/HF Cats, Corsa Catback, 219/230 .606/.608 115+3, Patriot Gold springs, LS7 MAF, ZR1 MAP, 160 stat, Melling HF/HV Oil pump, B&M Trans Cooler, Snow Stage 3, RPM 505 19's staggered 275R & 245F Continental Extreme Contact DW, Eibach Springs, Koni Struts, Lovells bushes, BMR Sways, eBay Catch Can, HID's, lot's of audio improvements & interior stuff.