Actually, the problem is it's a Ford product. That is not sarcasm. Ford has a real lot of problems with their power steering systems when the fluid runs empty. There are all kinds of specialty tools on the market to aid in bleeding the air out of the system. Until that happens, the buzzing and groaning noises can be expected, and it is real common for fluid to be burped out when you stop the engine. When the power steering pump stops running, the highly-compressed air in the system expands and pushes the fluid out of the reservoir.
One of the more popular special tools is not much more than a funnel that attaches to the fluid reservoir. It catches the fluid that burps out, and directs it back into the reservoir.
Part of the problem is the air in the system gets compressed, then it becomes trapped in high spots where it can't flow out and back to the reservoir. What may help is to park with one side of the van higher than the other side, then stop the engine. The air will expand, then some of it will be pushed to the reservoir the next time the engine is started and you turn the steering wheel. Do that again with the other side higher.
Normally, for all other car brands, we just run the steering wheel from full-left to full-right a few times, and the system is bled. In a few unusual cases, we have to run the steering wheel back and forth while one side is up higher, but that is done with the engine running. It's only on Ford products that bleeding can be a very frustrating multi-day affair, so don't be too fast to blame the repair shop. Check the fluid level a few times per day, and don't allow it to get low enough that more air is drawn in by the pump.
Tuesday, April 4th, 2017 AT 4:56 PM