I have a '06 Mazda3 that since winter has developed a noise right after start-up. Since I don't have any experience on what lifters or valve noise sound like, I can only say it's not a tick or ping but a continuous churning that is louder than what I am used to during idling. No temperature spikes or leaking fluids of any kind. No idle fluctuations. No hesitation during starts from stops. I moved into a MidAtlantic region condo garage that is covered but not enclosed (after having an enclosed garage the last 3 years). Noticed that the noise, at first, is prevalent on most damp colder overnights. The car now seem to routinely have this noise whether air is dry or moist. However, after 5 minutes driving, it disappear is eerily quiet when warm & there is no trace of the noise. My questions are: 1) What can it be? 2) How can I reproduce this noise to get it professionally diagnose esp. if I drive to a shop more than 5 mins away? 3) If lifters/valves - can oil solve the issue? Thanks for any insights.