They should at least narrow the ticking down to it's source: Does it tick at engine RPM, or half? (the valve train operates at half the engine RPM). Is the ticking from an exhaust leak? Did they pull plug wires one at a time with engine running to determine if ticking is from a particular cylinder? Is this a high mileage motor? What sort of oil are you using? Personally, I'd do the flush, Seafoam or Lucas. Badly gunked lifters aren't really going to get that clean with just a flush, they may need to be replaced, or at least taken out and cleaned and evaluated. You should also check oil pressure, if this is a worn motor lack of oil pressure may be causing some engine noise.