Engine makes squeaky noises!

Good day Dear motor talk community (friends) Have a squeaky noise at the Micra when the engine is running – also when briefly gasing – WAPU, belts, reversing wheels renewed. No change. I have run the engine without aggregates and belts – noise remains (like a broken WAPU). Are three mechanics and with our Latin at the end! Noise is sometimes louder and then again briefly away. Comes about after 3-5 min. after starting and from the lower half of the engine. I would be grateful for a tip! Greetings from Vienna