Federal banking regulators are growing more and more uneasy over the apparent slackening of underwriting rules for so-called affordability mortgage products, prompting calls to lenders to pay closer attention to risks associated with such loans. Regulators are eyeing interest-only loans, negative amortization features, and second mortgages with high loan-to-value ratios with great concern. With market competition for such loans growing tighter, regulators are worried that lenders are easing their underwriting rules to pump up their…