I only use 250mg acetyl-Carnitine from Puritan's. Because carnitine is not well absorbed per dose, it is best to use smaller doses more often during the day that one big large one. The acetyl group can cleave off
acetyl carnitine, during storage, creating acetic acid (which is in vinegar). If you smell this vinegar odor from the storage bottle, then your carnitine has been stored wrong or out of date.

I don't have problems with either R-lipoic or carnitine. But then I always take things orally with lots of water.

Heartburn may signal a poor lining in the stomach ... long ago when we all started Omega-3's... mostly because of my son's ADHD...over a decade ago...my then common GERD from my hiatal hernia was terrible. I was on Prilosec for it. Within 3 months of taking the essential fatty acids, it totally cleared up and stayed cleared up. Cox-1 prostaglandins are made from Omega-3s like flax oil, and one of their jobs is to maintain the mucus membranes in the lungs and GI tract. This is one reason that NSAIDs will cause GI ulcers, because they block Cox-1 activity in the body. The development of the Cox-2 ones, of which only Celebrex remains, was to avoid the GI damage.
Bextra and Vioxx were taken off the market because they blocked some critical beneficial Cox-2 activities leading the increased heart attacks. That is just a little side factoid.