Getty Images The clock is ticking for stocks in 2018.Will 2018 be the year the stock market rally screeches to a halt? It may be, if those analysts who are cautioning that a bubble is forming in credit markets are right and companies are overextending themselves to a degree that could spell trouble ahead. Most analysts agree that the credit market has been speeding ahead at a bubble-like pace. Companies have been piling on debt in recent years to take advantage of low interest rates, or more recently, to get ahead of a series of well-telegraphed interest-rate hikes. If their borrowing is simply to refinance existing debt at lower interest rates, it’s a positive for balance sheets. But many companies have borrowed to raise funds for shareholder rewards, and that may come back to bite them if rates were to spike.via