Worrying news for anyone whose marriage appears to be a conflict-free zone: a lack of shouting matches could actually be a sign you're drifting apart. A three-year study of 40000 couples by the Marriage Foundation revealed last week that 60% of couples who split or divorced had reported they were "generally happy" just 12 months earlier. In fact, only 9% of relationships failed due to a period of high conflict or severe unhappiness."Sudden abrupt ends to a marriage, violence and arguments are less likely than slowly growing apart," agrees divorce lawyer Marilyn Stowe.Couples counsellor Carole Nyman believes that avoiding disagreements is a sure-fire route to developing "lumpy carpet syndrome" - where issues in a marriage are not addressed, but ignored, only to accumulate over time.Here are six other warning signs that might mean yours is on the rocks:Your spouse stops complainingNyman says "resentment is a number one killer of desire, in both genders". If you're married to a tortoise-type who would rather take shelter under their shell than argue their point, the unsuspecting partner may think that the issue has gone away. And if your partner has simply given up trying to explain themselves, they're probably still simmering away, without you realising.You both put your kids firstWork and children can place pressure on relationships and they inevitably have to come first, at times. But Stowe says that consistently channelling all your energies into your children, instead of each other, can backfire in the long term: "When children leave home, marriages which on the surface appear to be fine, often do end - because couples find there is nothing left."You're more interested in other couples than your own relationshipMaking comparisons with other couples is a tell-tale sign your own relationship might be suffering. "When we are unhappy, we tend to judge other couples as happier than us," says Nyman.Your friendships suddenly become more importantNot looking forward to an end-of-day debrief with your other half suggests your lines of communication are breaking down. Stowe says a sign to watch out for is "if you can't be bothered to talk to your spouse because the response is likely to be negative or uninteresting or a waste of time". This can result in finding others you prefer to confide in.You don't wonder what the other is thinkingStowe says that warning bells should ring if "it doesn't particularly matter to you what your spouse thinks or what might please him or her".Your sex drives are out of syncBoth Stowe and Nyman think changes to your sex routine are one of the first signs that something is not right.Besides an obvious loss of interest in sex, Nyman says to watch for "changes in love-making style, such as less concern for the partner, a change in who initiates, or less connection during sex". ..